The object of the present invention is to improve the performance of the processes for producing cold and/or heat by means of an absorption cycle. The principle of an absorption refrigerator is well known. The absorption cycle for producing cold basically comprises the following steps:
Cold is generated by vaporizing at a low pressure, a refrigeration fluid initially in the liquid form. This vaporized refrigeration fluid is then absorbed by a solvent phase while transmitting heat to an external medium. The resultant solution is heated at a higher pressure and a vapor phase of high refrigeration fluid content is generated. This vapor phase is condensed while transmitting heat to the external medium. A fraction of the resultant condensate may be fed back as reflux and contacted with the vapor phase in a rectifying zone in order to suppress the stripping of solvent and to obtain a practically pure condensed phase. The resultant condensed phase is expanded and vaporized again to generate cold. A cycle of this type commonly uses ammonia as the refrigeration fluid, and water as the solvent phase; however other solute-solvent pairs are also known.
The operation of a prior art system of this type is illustrated by the basic diagram of FIG. 1A. The refrigeration fluid is vaporized in the exchanger F while producing cold. The resultant vapor is fed through line 1 to the enclosure A where it is absorbed by a lean solution and the absorption heat is removed by an external fluid 2. A lean solution is intended to mean a solution having a relatively low concentration of the refrigeration fluid, and a concentrated solution is intended to mean a solution having a relatively high concentration of the refrigeration fluid. The concentrated solution obtained by absorption in the enclosure A is fed through the pump P.sub.1, the exchanger E.sub.1 and the duct 3 to the enclosure G. The enclosure G is heated with an external fluid 4 and a vapor phase is thus generated, which passes into the rectification zone R. The lean solution discharged from the enclosure G is passed through the duct 5 and the exchanger E.sub.1 where it re-heats the concentrated solution fed to the enclosure G; it is expanded through the valve V.sub.1 and fed to the enclosure A. The vapor discharged from the rectification zone R through the line 6 is condensed in the cooler C wherein it is cooled with an external fluid. A fraction of the condensed phase is fed back through the duct 7 to the rectification zone R as reflux and the remainder (line 8) is expanded through the valve V.sub.2 and vaporized in the exchanger F.
A device of this type may also work as a heat pump. In that case, heat generated in the absorption and condensation step is produced at a higher temperature than room temperature and can be used as heating means. The amount of heat thus produced is higher than the amount of heat consumed for generating the vapor phase. As a matter of fact, it also comprises the heat "pumped" from the exterior when vaporizing the refrigeration fluid in the exchanger F.
The absorption refrigerators are advantageous any time an unexpensive heat source is available, for example, excess steam in an industrial plant, or associated gas in the case of an oil field. However, plants of this type require, even for producing cold at a moderately low temperature level, for example at 0.degree. C., relatively large heat amounts. This heat consumption also results in an increase of the investments, particularly by requiring expensive condensation and heating exchangers.